3GPP allowed use of AMR and H.263 codecs in the ISO base media file format (MPEG-4 Part 12), because
3GPP specified the usage of the Sample Entry and template fields in the ISO base media file format as well as defining new boxes to which codecs refer.

The 3GPP file format specification was based on the QuickTime container format specification.

A 3GP file is always big-endian, storing and transferring the most significant bytes first.

First chunk must be of type "ftype" and has a sub-type at offset 8. 3GP defined by sub-type which must be one of values: "3ge6", "3ge7", "3gg6", "3gp1", "3gp2", "3gp3", "3gp4", "3gp5", "3gp6", "3gp7", "3gr6", "3gr7", "3gs6", "3gs7", "kddi".